厦门大学：《物理化学 Physical Chemistry》课程电子教案（PPT教学课件）反应动力学 Reaction-Kinetics（1/7）

Physical chemistr Reaction Kinetics(1) Xuan Cheng Xiamen University

1 Reaction Kinetics (1) Xuan Cheng Xiamen University Physical Chemistry

Ch ical chemistr Reaction Kinetic Reaction kinetics For example G/k- mol N2(g)+H2(g8)→NH3(g) 1663 H2(g)+O2(g)→H2O() 237.19 Thermodynamics: spontaneous reactions(possible to take place) Thermodynamics: can t answer (1) how to make them happen (2)how fast they will take place (3)the reaction mechanism

2 Physical Chemistry Reaction Kinetics ( ) ( ) 2 3 ( ) 2 1 N2 g + H2 g → NH3 g For example ( ) ( ) 2 1 ( ) 2 2 2 H g + O g → H O l 1 / −  G kJ mol o r -16.63 -237.19 Thermodynamics: spontaneous reactions (possible to take place) Thermodynamics: can’t answer (1) how to make them happen (2) how fast they will take place (3) the reaction mechanism Reaction Kinetics

Ch ical chemistr Reaction Kinetic Reaction kinetics Chemical Kinetics N2(g)+H2(g)→NH3(g) T.P. catalyst H2(g)+O2(g)→>H2O() T catalyst Chemical Kinetics The study of the rates and mechanisms of chemical reactions a reacting system is not in equilibrium

3 Physical Chemistry Reaction Kinetics ( ) ( ) 2 3 ( ) 2 1 N2 g + H2 g → NH3 g ( ) ( ) 2 1 ( ) 2 2 2 H g + O g → H O l T, P, catalyst T, catalyst Chemical Kinetics: Chemical Kinetics The study of the rates and mechanisms of chemical reactions A reacting system is not in equilibrium Reaction Kinetics

Ch ical chemistr Reaction Kinetic Rate of reaction Consider the homogeneous reaction(occurs entirely in one phase) aA+bB+…→>eE+fF+ (171) dn a/dt n B dnB /dt b a dt b di The rate of conversion j B anE F b dt (172) e At equilibrium, J=0

4 Physical Chemistry Rate of Reaction Consider the homogeneous reaction (occurs entirely in one phase) b a dn dt dn dt B A = / / aA+ bB +→ eE + fF + (17.1) The rate of conversion J dt dn dt f dn dt e dn dt b dn a J 1 A 1 B 1 E 1 F  − = − == = (17.2) dt dn dt b dn a 1 A 1 B = At equilibrium, J = 0 Reaction Kinetics

Ch ical chemistr Reaction Kinetic Rate of reaction The rate of reaction r (173) At constant v 1 d[a 1 d B 1 de 1 dF e dt (17 mol dms. mo cms

5 Physical Chemistry Rate of Reaction        = − dt dn V V a J r 1 1 A (17.3) = − = − == = = dt d F dt f d E dt e d B dt b d A a r 1 [ ] 1 [ ] 1 [ ] 1 [ ] (17.4)* At constant V The rate of reaction r mol dm-3 s -1 mol cm-3 s -1 Reaction Kinetics

Ch ical chemistr Reaction Kinetic R ate laws For many reactions r=k[4y[B2…[y (175) k: rate constant (rate coefficient),kfT, P) as B,.n: order or partial order a+B+..+h=n: overall order The expression for ras a function of concentrations at a fired temperature is called the rate law

6 Physical Chemistry Rate Laws For many reactions          r = k A B  L (17.5)* k: rate constant (rate coefficient), k = f (T, P) , , : order or partial order + +  +  n : overall order The expression for r as a function of concentrations at a fixed temperature is called the rate law. Reaction Kinetics

Ch ical chemistr Reaction Kinetic Reaction orders ero -or de er k First-order r=k乎Pr=[4B Se econd-order r=kAP[B] r=kAIBP Third-order k[AIB」 Negative First-order KAIB]/2 1. 5-order r=A42) No simple order

7 Physical Chemistry Reaction Orders o r = k r = kA   2 r = k A r = kAB r kA B 2 =    2 r = k A B    −2 r = k A B    1/ 2 r = k A B    (   ) 1/ 2 r = k A B / 1− B Zero-order First-order Second-order Third-order Negative First-order 1.5-order No simple order Reaction Kinetics

Ch ical chemistr Reaction Kinetic Rate laws Reaction Rate law klh, Br 1/2 H+B→2HB 1+jHBr[Br2 H2+2→>2团 kle2ll21 2N2O5>4MO2+02 CH2CHO→CH4+CO r=k[cH3CHOF/2

8 Physical Chemistry Rate Laws Reaction Rate Law H Br 2HBr 2 + 2 →        2 1/ 2 2 2 1 j HBr / Br k H Br r + = 2N2 O5 → 4NO2 +O2 H I 2HI 2 + 2 →    2 2 r = k H I   N2 O5 r = k CH3 CHO →CH4 +CO   3/ 2 r = k CH3 CHO Reaction Kinetics

Ch ical chemistr Reaction Kinetic Reaction mechanisms Reaction actually occurs 2SO2+O2-A,2O3 02+2AO→O (177) intermediate (O2)+SO2→MO+SO3 2N2O5>4MO2+O2 Elementary reaction Step(a) N2O令→NO2+MO3 Step(b NO2+NO3→NO+O2+NO2 (178) Step(c) NO+NO3→>2NO2

9 Physical Chemistry Reaction Mechanisms NO2 + SO2 → NO+ SO3 O2 + 2NO →2NO2 (17.7) 2SO2 O2 2SO3 NO + ⎯ ⎯→ intermediate 2N2 O5 → 4NO2 +O2 N2 O5  NO2 + NO3 NO+ NO3 → 2NO2 NO2 + NO3 → NO+O2 + NO2 (17.8) Step (a) Step (b) Step (c) Elementary reaction Reaction actually occurs Reaction Kinetics

choical Chemistry Reaction Kinetic Measurement of reaction rates The concentration of a reactant or product as a function of time Chemical method Cooling the sample removing a catalyst Diluting the mixture At constant T Adding a species At intervals Slows down or stop the reaction Rapidly analyze chemical Reaction vessels compositions of the mixture

10 Physical Chemistry Measurement of Reaction Rates Chemical Method The concentration of a reactant or product as a function of time Reaction vessels At constant T At intervals Slows down or stop the reaction Rapidly analyze chemical compositions of the mixture Cooling the sample removing a catalyst Diluting the mixture Adding a species Reaction Kinetics